Eruption age of the Kusandong Tuff in the Cretaceous Gyeongsang Basin, Korea

Abstract

The Kusandong Tuff has been regarded as a key bed for the subdivision of the Upper Cretaceous strata in the Gyeongsang Basin. Since the Kusandong Tuff has the wide range of the K-Ar whole-rock ages (82 similar to 103 Ma) due to contamination and alteration, it is difficult to estimate the eruption age of the tuff. For the precise eruption age of the Kusandong Tuff, zircon grains from the tuff were analyzed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The zircon U-Pb ages of the Kusandong Tuff are 97.1 +/- 2.0 Ma and 97.3 +/- 1.8 Ma, indicating that the tuffaceous bed formed during the middle Cenomanian. Accidental zircons in the tuff have a U-Pb age of 107. 3.0 Ma, which corresponds to the earlier Cretaceous igneous activity during the early Albian in age.